In U.S. Pat. No. 3,980,713 there is described a method for the production of distyryl-biphenyl fluorescent whitening agents comprising reacting 1 mole of 4,4'-diiodobiphenyl with 2 mols of a styrene compound, such as a styrene sulfonic acid, in the presence of a palladium catalyst and a base at elevated temperature. The styrene sulfonic acid reactant is produced by sulfonation of styrene, which results in a mixture of 2- and 4-styrene sulfonic acid. If a sulfonated distyryl-biphenyl fluorescent whitening agent of specific structure is desired, however, this mixture must be subjected to a separation procedure, prior to reaction with 4,4'-diiodobiphenyl. Other processes which are disclosed for the production of the styrene compound reactants are the dehydration of an approriate ethylbenzene, the cleaving off of hydrogen halide from a halogenoalkylbenzene or the reaction of ethylene with a bromo- or iodobenzene in the presence of a palladium catalyst and a base.
A new route to the compounds of formula (1) has now been found which uses a simpler process for the production of the styrene reactant and which provides high yields of the end products of formula (1).